Method for preparing a composition comprising functionalised mineral particles and corresponding composition

ABSTRACT

A method for preparing a composition including mineral particles functionalized by at least one organic group and having a specific surface defined according to the BET method greater than 500 m 2 /g, involves: —choosing a phyllosilicate composition, including mineral particles having a thickness of less than 100 nm, a largest dimension of less than 10 μm and belonging to the family of lamellar silicates; —choosing at least one functionalizing agent, from the group formed from the oxysilanes and oxygermanes having at least one organic group, —bringing the phyllosilicate composition into contact with a functionalizing solution including the functionalizing agent, so as to obtain a phyllosilicate composition including mineral particles functionalized by the organic group, while choosing the organic group from the group formed from the cationic heteroaryl groups, the quaternary ammonium groups and the salts of same. The phyllosilicate composition obtained by the method is also described.

The invention relates to a method for preparing a composition comprisingmineral particles functionalised by at least one organic group, and to acomposition comprising mineral particles functionalised by at least oneorganic group.

Many minerals such as borates or silicates are used in variousindustrial fields.

Natural talc, for example, is a hydroxylated magnesium silicate of theformula Si₄Mg₃O₁₀(OH)₂ belonging to the phyllosilicate family. Thephyllosilicates are composed of an irregular stack of elementarylamellae of crystalline structure, the number of which varies fromseveral units to several tens of units. Among the phyllosilicates(lamellar silicates), the group comprising especially talc, mica andmontmorillonite is characterized by the fact that each elementarylamella is constituted by the association of two tetrahedral layerssituated on either side of an octahedral layer. This group correspondsto the 2:1 phyllosilicates, which include especially the smectites. Inview of their structure, the 2:1 phyllosilicates are also described asbeing of the T.O.T. (tetrahedron-octahedron-tetrahedron) type.

The octahedral layer of the 2:1 phyllosilicates is formed of two planesof O²⁻ and OH⁻ ions (in the molar proportion O²⁻/OH⁻ of 2/1). On eitherside of this middle layer there are two-dimensional lattices oftetrahedrons, of which one of the vertices is occupied by an oxygen ofthe octahedral layer, while the other three are occupied bysubstantially coplanar oxygens.

Phyllosilicate mineral particles, such as talc, are used in the form offine particles in many industrial sectors, for example: rubber,thermoplastics, paper, paints, pharmaceuticals, cosmetics, or alsophytosanitary products. They are used as an inert filler (for theirchemical stability or also to dilute more expensive active compounds) oras functional fillers (for example to enhance the mechanical propertiesof some materials). When they are introduced into such materials, theirdispersion frequently presents difficulties, especially becausephyllosilicate mineral particles have a small particle size. The finestmineral particles in fact tend to agglomerate, reducing the effects thattheir use is expected to have on the final properties of the materials.

In order to remedy these problems, the invention aims to propose amethod for preparing a composition comprising mineral particlesfunctionalised by at least one organic group.

The invention aims also to propose such a method which can be carriedout simply and quickly and which is compatible with the constraints ofindustrial exploitation.

The invention aims also to propose a composition comprising mineralparticles functionalised by at least one organic group.

The invention aims also to propose compositions comprising syntheticphyllosilicate mineral particles which can be used as a replacement fornatural talc compositions.

To that end, the invention relates to a method for preparing acomposition comprising mineral particles functionalised by at least oneorganic group and having a specific surface area determined according tothe BET method—standard AFNOR X 11—621 and 622—of greater than 500 m²/g,wherein:

-   -   there is chosen a composition, named the phyllosilicate        composition, comprising mineral particles belonging to the        family of the lamellar silicates, said mineral particles having        a thickness of less than 100 nm and a largest dimension of less        than 10 μm;    -   there is chosen at least one compound, named the functionalising        agent, from the group formed of oxysilanes and oxygermanes        having at least one organic group;    -   said phyllosilicate composition is brought into contact with a        solution, named the functionalising solution, comprising said        functionalising agent, so as to obtain a phyllosilicate        composition comprising mineral particles functionalised by said        organic group, characterised in that the organic group is chosen        from the group formed of cationic heteroaryl groups, quaternary        ammonium groups and their salts.

The inventors have found, surprisingly, that it is possible by means ofa method according to the invention, in which phyllosilicate mineralparticles are brought into contact with at least one such functionalisedoxysilane and/or with at least one such functionalised oxygermane, toobtain functionalised mineral particles whose tendency to agglomerate isreduced considerably.

Throughout the text, “heteroaryl group” is understood as meaning anygroup that contains one or more aromatic rings having from 5 to 18 ringmembers and that contains from 1 to 6 heteroatoms (chosen from oxygen,nitrogen and sulfur).

The cationic heteroaryl groups which can be carried by said oxysilanesand oxygermanes are, for example, imidazolium groups, pyridinium groupsor also indolinium groups.

Throughout the text, “quaternary ammonium group” is understood asmeaning any group of the formula N⁺R₁₀R₁₁R₁₂R₁₃ wherein R₁₀, R₁₁, R₁₂and R₁₃ are identical or different and are chosen from a hydrogen atomand linear or branched alkyl groups containing from 1 to 18 carbonatom(s).

Advantageously, in a variant of a method according to the invention, themineral particles are chosen from the group of the non-swelling 2:1phyllosilicates. Some of the non-swelling 2:1 phyllosilicates (forexample mica) have a cation in the interfoliar space, and others (forexample talc) have an interfoliar void and do not permit interfoliarcation exchange. “Interfoliar void” is understood as meaning the factthat such non-swelling 2:1 phyllosilicates are free of any interfoliarcation, of any interfoliar anion and of any interfoliarmolecule—especially water molecule.

Advantageously and according to the invention, said functionalisingagent has the chemical formula:

wherein:

-   -   A denotes said organic group,    -   T is chosen from the group formed of silicon and germanium, and    -   R1, R2 and R3 are identical or different and are chosen from the        group formed of hydrogen and linear alkyl groups containing from        1 to 3 carbon atom(s).

Advantageously and according to the invention, said organic group(organic group A) has the chemical formula:

wherein:

-   -   R7 is chosen from linear or branched alkyl groups containing        from 1 to 18 carbon atom(s),    -   n is an integer from 3 to 11,    -   X⁻ is an anion chosen from the group formed of the bromide ion,        the iodide ion, the chloride ion, the trifluoromethanesulfonate        anion, the acetate anion, the nitrate anion and the nitrite        anion.

Advantageously and according to the invention, R7 is chosen from thegroup formed of linear alkyl groups and branched alkyl groups containingfrom 1 to 18 carbon atom(s), especially from 1 to 10 carbon atom(s) andin particular from 1 to 4 carbon atom(s).

Advantageously, A is a cationic group which is soluble in an aqueousmedium, A contributes towards conferring a water-soluble nature uponsaid oxysilane and/or said oxygermane.

More particularly, R1, R2 and R3 each represent a methyl (—CH₃) or ethyl(—CH₂—CH₃) group. Accordingly, in a particularly advantageous variant ofa method according to the invention, said oxysilane has the formula:

wherein X⁻ is an anion wherein X is chosen from the group formed ofchlorine, iodine and bromine. In this case, the oxysilane (atrialkoxysilane) is a 1-(trimethoxy-silyl-propyl)-3-methyl-imidazoliumsalt.

Advantageously and according to the invention, said functionalisingagent is chosen from the group formed of oxysilanes and oxygermaneswhich are soluble in an aqueous medium. In particular, advantageouslyand according to the invention, said oxysilanes and said oxygermanes areat least partially soluble in water and optionally soluble in anyproportions in water.

Advantageously and according to the invention, said functionalisingsolution is an aqueous solution.

Accordingly, a method according to the invention does not require theuse of organic solvents which are dangerous to humans or to theenvironment but can be carried out wholly advantageously in an aqueousmedium.

Throughout the text, “aqueous medium” denotes any liquid mediumcomprising water and optionally one or more other solvent(s) that aremiscible with water. It can be, for example, an aqueous-alcoholic mediumcomprising water and ethanol.

Advantageously and according to the invention, there is chosen aphyllosilicate composition comprising mineral particles from the groupformed of talcs, pyrophyllites, micas (such as muscovite, paragonite oralso illite), smectites (such as montmorillonite, saponite, hectorite oralso beidellite), kaolinites, serpentinites, chlorites and mixturesthereof.

Advantageously and according to the invention, said phyllosilicatecomposition comprises mineral particles having the chemical formula:

(Si_(x)Ge_(1-x))₄M₃O₁₀(OH)₂

-   -   Si denoting silicon,    -   Ge denoting germanium,    -   x being a real number of the interval [0; 1], and    -   M denoting a metal (metal atom), and especially M denoting at        least one divalent metal having the formula        Mg_(y(1))Co_(y(2))Zn_(y(3))Cu_(y(4))Mn_(y(5))Fe_(y(6))Ni_(y(7))Cr_(y(8));        each y(i) representing a real number of the interval [0; 1], and        such that

${\sum\limits_{i = 1}^{8}\; {y(i)}} = 1.$

In a particularly advantageous variant of a method according to theinvention, said phyllosilicate composition that is used comprisesparticles of talc having the chemical formula Si₄Mg₃O₁₀(OH)₂.

Advantageously and according to the invention, said mineral particleshave a thickness of less than 100 nm and a largest dimension of lessthan 10 μm. Advantageously and according to the invention, saidparticles have a thickness of from 1 nm to 150 nm, in particular from 5nm to 50 nm, and a largest dimension of from 20 nm to 10 μm.

Throughout the text, “thickness” of the silicate mineral particlesdenotes the smallest dimension of said particles, that is to say thedimension of said particles in direction c of the crystal lattice ofsaid silicate mineral particles.

Throughout the text, “largest dimension” of the silicate mineralparticles denotes the largest dimension of said particles in the plane(a, b) of the crystal lattice of said silicate mineral particles.

The thickness and the largest dimension of the silicate mineralparticles are measured by observation by scanning electron microscopy(SEM) or by transmission electron microscopy (TEM).

In a method according to the invention, the duration of thefunctionalising step during which said phyllosilicate composition isbrought into contact with at least one functionalising agent (oxysilaneand/or oxygermane), the concentration of each functionalising agent inthe functionalising solution, and the temperature at which this steptakes place are adapted to permit fixing of said organic group to thephyllosilicate mineral particles of said phyllosilicate composition, andtherefore functionalisation of the phyllosilicate composition.Advantageously and according to the invention, said predeterminedduration, during which said phyllosilicate composition is brought intocontact with the functionalising solution, is from 5 seconds to 30 daysand in particular from 5 minutes to 2 hours.

Advantageously and according to the invention, the concentration ofoxysilane(s) and/or oxygermane(s) present in the functionalisingsolution is from 0.005 mol/l to the saturation concentration thereof inthe medium.

The concentration of oxysilane(s) and/or oxygermane(s) present in thefunctionalising solution is, for example, from 0.01 mol/l to 3 mol/l.

Advantageously and according to the invention, the functionalisingagent(s) and the phyllosilicate mineral particles are brought intocontact in the functionalising solution in such a manner that the molarratio between the functionalising agent(s) and the phyllosilicatemineral particles (number of moles of oxysilane(s) and/oroxygermane(s)/number of moles of phyllosilicate mineral particles) isfrom 0.01 to 0.5, especially from 0.05 to 0.3.

Furthermore, advantageously and according to the invention, thefunctionalising step takes place at a temperature of from 5° C. to 100°C. The contacting which takes place in this step of a method accordingto the invention can be carried out, for example, at ambient temperature(from 20° C. to 25° C.) or also at a temperature slightly above ambienttemperature, for example from 25° C. to 40° C.

The functionalising step can be carried out with or without stirring. Inparticular, advantageously and according to the invention, saidphyllosilicate composition is brought into contact with thefunctionalising solution with stirring, for example with magneticstirring by means of a magnetic stirrer.

At the end of the functionalising step of a method according to theinvention, the functionalised phyllosilicate composition obtained can berecovered by removing the aqueous functionalising solution. The aqueousfunctionalising solution can be removed, for example, after spontaneousdecantation of said functionalised phyllosilicate composition (byallowing the solution to rest) and removal of the supernatant solutionor also by centrifugation of the functionalising solution comprisingsaid functionalised phyllosilicate composition obtained. Thefunctionalised phyllosilicate composition comprising functionalisedphyllosilicate mineral particles that is recovered can then be rinsed soas to remove the residual oxysilanes and/or oxygermanes. Accordingly,advantageously, in a method according to the invention, following thefunctionalising step, the functionalised phyllosilicate mineralparticles obtained are rinsed with an aqueous solution which is at leastsubstantially free of oxysilanes and oxygermanes.

At the end of the functionalising step of a method according to theinvention, the functionalised phyllosilicate composition obtained can bestored or used as it is, in the form of a gel or aqueous suspension, orit can also be dried so as to remove at least in part the aqueoussolution, especially water, still present. Advantageously and accordingto the invention, the functionalised phyllosilicate mineral particlesobtained are dried after functionalisation, and before or after optionalrinsing. Drying can be carried out by any drying means which allows theaqueous solution to be removed. Drying can, for example, be carried outdirectly in an oven (for example at a temperature of approximately 100°C.), by spraying, by drying by means of microwave irradiation, or alsoby lyophilisation.

In addition, it is possible to repeat at least once said functionalisingstep in which the phyllosilicate composition is brought into contactwith the functionalising solution. In this manner it is possible tomodify to a greater or lesser extent the rate of functionalisation (orgrafting rate) of the phyllosilicate composition.

After the mineral particles of the phyllosilicate composition have beenfunctionalised, it is also possible to carry out an at least partialexchange of the anion X⁻. Accordingly, advantageously and according tothe invention, after said phyllosilicate composition has been broughtinto contact with the functionalising solution, there is carried out anat least partial exchange of the anion X⁻ by at least one anionicspecies which is different from X⁻ and is chosen from the group formedof the bromide ion Br⁻, the iodide ion I⁻, the chloride ion, thebis(trifluoromethanesulfonyl)amide anion, the trifluoromethanesulfonateanion, the hexafluorophosphate anion, the tetrafluoroborate anion, theacetate anion, the nitrate anion NO₃ ⁻ and the nitrite anion NO₂ ⁻. Suchan exchange by metathesis allows the more or less hydrophilic orhydrophobic nature of the functionalised mineral particles that areprepared to be modulated in a customised manner. Thebis(trifluoromethanesulfonyl)amide anion has, for example, a highlyhydrophobic nature.

Furthermore, after the mineral particles of the phyllosilicatecomposition have been functionalised, it is possible in particular tocarry out an at least partial exchange of the anion X⁻, when X is chosenfrom the group formed of chlorine, bromine and iodine, by bringing saidfunctionalised mineral particles into contact with a solution comprisinga metal salt, in particular a silver salt (AgNO₃, for example).Advantageously and according to the invention, after said phyllosilicatecomposition has been brought into contact with the functionalisingsolution, there is carried out an at least partial exchange of the anionX⁻, when X is chosen from the group formed of chlorine, bromine andiodine, by adding at least one silver salt, in particular awater-soluble silver salt. In this manner, by allowing the solutioncomprising said functionalised mineral particles and said silver salt toage, the formation of nanometric particles of silver associated with themineral particles is observed, the nanometric particles having theadvantage of having bactericidal properties.

Advantageously and according to the invention, said phyllosilicatemineral particles are prepared by a hydrothermal treatment of a hydrogelprecursor containing silicon and/or germanium and a metal, said hydrogelprecursor comprising particles of the formula (Si_(x)Ge_(1-x))₄M₃O₁₁,n′H₂O, wherein:

-   -   Si denotes silicon,    -   Ge denotes germanium,    -   x is a real number of the interval [0; 1],    -   M denotes at least one—especially one—metal atom,    -   n′ relates to a number of molecule(s) of water associated with        said hydrogel.

In particular, the metal M is chosen from the group formed of magnesium,cobalt, zinc, copper, manganese, iron, nickel and chromium.

According to another formulation, the hydrogel precursor comprises:

-   -   4 silicon and/or germanium atoms according to the following        chemical formula: 4 (Si_(x)Ge_(1-x)), x being a real number of        the interval [0; 1],    -   3 atoms of metal M, M denoting at least one divalent metal        having the formula Mg_(y(1))Co_(y(2))        Zn_(y(3))Cu_(y(4))Mn_(y(5))Fe_(y(6))Ni_(y(7))Cr_(y(8)), wherein        each y(i) represents a real number of the interval [0; 1], and        such that

${{\sum\limits_{i = 1}^{8}\; {y(i)}} = 1},$

-   -   (10−ε) oxygen atoms ((10−ε) O), ε being a real number of the        interval [0; 1],    -   (2+ε) hydroxyl groups ((2+ε) (OH)), ε being a real number of the        interval [0; 1].

The hydrogel precursor therefore corresponds to the following chemicalformula (II):

4(Si_(x)Ge_(1-x))3M((10−ε)O)((2+ε)(OH))  (II).

Water molecules can further be bonded to the particles of the hydrogelprecursor. These are water molecules adsorbed or physisorbed onto theparticles of hydrogel precursor and not constituent water molecules thatare usually present in the interfoliar spaces of certain phyllosilicateparticles.

Throughout the text, “hydrothermal treatment under pressure” denotes anytreatment carried out in a closed receptacle, such as an autoclave, inthe presence of water, at a predetermined temperature and at a pressuregreater than atmospheric pressure.

The duration of the hydrothermal treatment is adapted to allow saidphyllosilicate mineral particles to be obtained, as a functionespecially of the temperature at which the hydrothermal treatment iscarried out. Advantageously and according to the invention, saidhydrothermal treatment is carried out for a duration of from 1 second to60 days, especially from 30 minutes to 24 hours.

Advantageously and according to the invention, the hydrothermaltreatment of said hydrogel precursor is carried out in a vessel with aconstant volume, for example by means of an autoclave. It can be, forexample, an autoclave formed of a nickel-based alloy such as Hastelloy®(marketed by Haynes International, Kokomo, United States) or also anautoclave made of titanium or optionally of steel with an inner liningof polytetrafluoroethylene (PTFE). Such an autoclave can have anycapacity, for example a capacity ranging from 200 ml to 50 litres.

The hydrothermal treatment can be carried out with or without mechanicalstirring. In a particularly advantageous variant of a method accordingto the invention, said hydrothermal treatment is carried out withmechanical stirring. There can be used for that purpose, for example, anautoclave equipped with an internal metal propeller.

Advantageously and according to the invention, said hydrothermaltreatment is carried out at a pressure of from 0.5 MPa (5 bar) to 20 MPa(200 bar). Advantageously and according to the invention, saidhydrothermal treatment is carried out under autogenous pressure, that isto say at a pressure that is at least equal to the saturation vapourpressure of water (pressure at which the vapour phase is in equilibriumwith the liquid phase). The autogenous pressure reached in the autoclaveduring the hydrothermal treatment therefore depends especially on thetemperature at which said hydrothermal treatment is carried out, on thevolume of the autoclave and on the quantity of water present. It islikewise possible to carry out the hydrothermal treatment at a pressuregreater than the saturation vapour pressure of water or greater than theautogenous pressure in the receptacle in which the hydrothermaltreatment is taking place. To that end, a gas that is chemically neutralwith respect to the hydrothermal reaction is injected into the autoclaveor the receptacle in which the hydrothermal treatment is taking place.Such a gas is chosen from the group formed of the inert gases (raregases), in particular argon, dinitrogen (N₂), carbon dioxide and air(compressed air).

Advantageously and according to the invention there is added to theautoclave, with said hydrogel precursor, a quantity of water (preferablyof distilled water) which is at least sufficient to create, inside theautoclave brought to the treatment temperature, a saturation vapouratmosphere.

Advantageously and according to the invention, the hydrothermaltreatment is carried out using a liquefied hydrogel precursor having aliquid/solid ratio of from 2 to 20, especially from 5 to 15 (thequantity of liquid being expressed in cm³, and the quantity of solidbeing expressed in grams and denoting the quantity of hydrogel only). Ifnecessary, an appropriate amount of water for achieving that ratio maybe added to said liquefied hydrogel precursor.

Advantageously and according to the invention, the hydrogel precursor isprepared by a coprecipitation reaction between:

-   -   at least one compound comprising silicon and/or germanium, such        as sodium metasilicate or sodium metagermanate or also silicon,        and    -   at least one metal salt,        so as to obtain a hydrated hydrogel precursor containing silicon        and/or germanium and a metal and containing 4 silicon and/or        germanium atoms for 3 atoms of at least one metal M.

Advantageously and according to the invention, said metal salt used forthe preparation of the hydrogel precursor is chosen from the metal saltsof magnesium, cobalt, zinc, copper, manganese, iron, nickel and/orchromium can be used in a method according to the invention. Inparticular, advantageously and according to the invention, said metalsalt is chosen from the metal chlorides (of the formula MCl₂) and themetal acetates (of the formula M(CH₃COO)₂) (M being chosen from thegroup formed of magnesium, cobalt, zinc, copper, manganese, iron, nickeland chromium) and the metal sulfates. Preferably, said metal salt ischosen from MgCl₂, CoCl₂, ZnCl₂, CuCl₂, MnCl₂, FeCl₂, NiCl₂, CrCl₂ andMg(CH₃COO)₂, Co(CH₃COO)₂, Zn(CH₃COO)₂, Cu(CH₃COO)₂, Mn(CH₃COO)₂,Ni(CH₃COO)₂ and Cr(CH₃COO)₂.

In a variant embodiment according to the invention, the coprecipitationreaction of the hydrogel precursor and/or the hydrothermal treatment ofthe hydrogel precursor is/are carried out in the presence of acarboxylate salt. It is in particular a carboxylate salt of the formulaR8-COOM′, wherein:

-   -   M′ denotes a metal chosen from the group formed of Na and K, and    -   R8 is chosen from the group formed of H and alkyl groups        containing fewer than 5 carbon atoms.

The invention relates also to a composition obtainable by a methodaccording to the invention.

The invention therefore relates also to a composition, named aphyllosilicate composition, comprising mineral particles belonging tothe family of the lamellar silicates, characterised in that said mineralparticles have:

-   -   a thickness of less than 100 nm and a largest dimension of less        than 10 μm;    -   a specific surface area determined according to the BET        method—standard AFNOR X 11—621 and 622—of greater than 500 m²/g;        and    -   at least one organic group chosen from the group formed of        cationic heteroaryl groups, quaternary ammonium groups and their        salts.

Advantageously and according to the invention, said phyllosilicatecomposition comprises mineral particles having the chemical formula:

(Si_(x)Ge_(1-x))₄M₃O₁₀(OH)₂

-   -   Si denoting silicon,    -   Ge denoting germanium,    -   x being a real number of the interval [0; 1],    -   M denoting a metal, and in particular at least one divalent        metal having the formula Mg_(y(1))Co_(y(2))        Zn_(y(3))Cu_(y(4))Mn_(y(5))Fe_(y(6))Ni_(y(7))Cr_(y(8)); each        y(i) representing a real number of the interval [0; 1], and such        that

${\sum\limits_{i = 1}^{8}\; {y(i)}} = 1.$

Advantageously and according to the invention, said mineral particleshave a thickness of less than 100 nm and a largest dimension of lessthan 10 μm.

Advantageously and according to the invention, said mineral particles(that is to say the functionalised mineral particles) have a specificsurface area of greater than 500 m²/g, especially greater than 600 m²/gand in particular greater than 700 m²/g.

Advantageously and according to the invention, said functionalisedmineral particles comprise from 0.001 millimole to 4 millimoles of saidorganic group per gram of mineral particles.

The invention relates also to a method for treating a compositioncomprising synthetic mineral particles and to a composition comprisingsynthetic mineral particles characterised in combination by all or someof the features mentioned hereinabove or hereinbelow.

Other objects, advantages and features of the invention will becomeapparent upon reading the description and the examples which follow andwhich make reference to the accompanying figures.

FIG. 1 shows an RX diffractogram of a composition according to theinvention on which there is shown the relative intensity of the signal(number of counts per second) as a function of the interplanar spacingin angstroms.

FIG. 2 shows a proton NMR spectrum of a composition according to theinvention, carried out by means of a BRUKER® Avance 400® spectrometer.

FIG. 3 shows a carbon NMR spectrum of a composition according to theinvention, carried out by means of a BRUKER® Avance 400® spectrometer.

FIG. 4 shows a silicon NMR spectrum of a composition according to theinvention, carried out by means of a BRUKER® Avance 400® spectrometer.

FIG. 5 shows an image obtained by field effect scanning electronmicroscopy of a composition according to the invention.

A phyllosilicate composition used in a method according to the inventioncan be prepared, for example, according to the following synthesisprotocol.

A/—General Protocol for Synthesis of a Composition Used in a MethodAccording to the Invention

1/—Preparation of a Hydrogel Precursor Containing Silicon and/orGermanium and a Metal

According to a first variant, the hydrogel containing silicon and/orgermanium and a metal is prepared by a coprecipitation according to thefollowing reaction equation:

$\left. {{4\begin{pmatrix}\left( {{Na}_{2}{OSiO}_{2}} \right)_{x} \\\left( {{Na}_{2}{OGeO}_{2}} \right)_{1 - x}\end{pmatrix}} + {2{HCl}} + {{mH}_{2}O} + {3\begin{pmatrix}{{y_{(1)}\left( {MgCl}_{2} \right)} + {y_{(2)}\left( {CoCl}_{2} \right)} + {y_{(3)}\left( {ZnCl}_{2} \right)} +} \\{{y_{(4)}\left( {CuCl}_{2} \right)} + {y_{(5)}\left( {MnCl}_{2} \right)} + {y_{(6)}\left( {FeCl}_{2} \right)} +} \\{{y_{(7)}\left( {NiCl}_{2} \right)} + {y_{(8)}\left( {CrCl}_{2} \right)}}\end{pmatrix}}}\rightarrow{\quad{\left\lbrack {{\left( {{Si}_{x}{Ge}_{1 - x}} \right)_{4}M_{3}O_{11}},{n^{\prime}H_{2}O}} \right\rbrack + {8{NaCl}} + {\left( {m - n^{\prime} + 1} \right)H_{2}O}}} \right.$

This coprecipitation reaction allows a hydrated hydrogel containingsilicon and/or germanium and a metal having the stoichiometry of talc (4silicon (Si) and/or germanium (Ge) atoms for 3 atoms of said divalentmetal M) to be obtained.

It is carried out starting from:

-   1. an aqueous solution of penta-hydrated sodium metasilicate or an    aqueous solution of sodium metagermanate, or a mixture of these two    solutions in the molar proportions x:(1−x),-   2. a metal chloride solution prepared with one or more metal salts    (in the form of hygroscopic crystals) diluted in distilled water,    and-   3. a 1N hydrochloric acid solution.

The hydrogel containing silicon and/or germanium and a metal is preparedaccording to the following protocol:

-   1. the hydrochloric acid solution and the metal chloride solution    are mixed,-   2. this mixture is added to the sodium metasilicate and/or    metagermanate solution; the coprecipitation gel forms instantly,-   3. the gel is recovered after centrifugation (at 7000    revolutions/minute for 15 minutes) and removal of the supernatant    (sodium chloride solution that has formed),-   4. the gel is washed with distilled or osmosed water or with tap    water (a minimum of two cycles of washing/centrifugation are    necessary).

According to a second variant, the hydrogel containing silicon and/orgermanium and a metal can be prepared by a coprecipitation reactioninvolving, as reagent, at least one compound comprising silicon, atleast one dicarboxylate salt of the formula M(R9-COO)₂ (R9 being chosenfrom H and alkyl groups containing fewer than 5 carbon atoms) in thepresence of at least one carboxylate salt of the formula R8-COOM′,wherein M′ denotes a metal chosen from the group formed of Na and K, andR8 is chosen from the group formed of H and alkyl groups containingfewer than 5 carbon atoms.

This coprecipitation reaction allows a hydrated hydrogel containingsilicon and/or germanium and a metal having the stoichiometry of talc (4Si/Ge for 3 M, M having the formulaMg_(y(1))Co_(y(2))Zn_(y(3))Cu_(y(4))Mn_(y(5))Fe_(y(6))Ni_(y(7))Cr_(y(8));each y(i) representing a real number of the interval [0; 1], and suchthat

$\left. {{\sum\limits_{i = 1}^{8}\; {y(i)}} = 1} \right)$

to be obtained.

The hydrogel containing silicon and/or germanium and a metal is preparedby a coprecipitation reaction carried out starting from:

-   1. an aqueous solution of penta-hydrated sodium metasilicate or an    aqueous solution of sodium metagermanate, or a mixture of these two    solutions in the molar proportions x:(1−x),-   2. a solution of dicarboxylate salt(s) prepared with one or more    dicarboxylate salt(s) of the formula M(R9-COO)₂ diluted in a    carboxylic acid, such as acetic acid, and-   3. a solution of carboxylate salt(s) prepared with one or more    carboxylate salt(s) of the formula R8-COOM′ diluted in distilled    water.

The hydrogel containing silicon and/or germanium and a metal is preparedaccording to the following protocol:

-   1. the sodium metasilicate solution and the solution of carboxylate    salt(s) of formula R8-COOM′ are mixed,-   2. the solution of dicarboxylate salt(s) of the formula M(R9-COO)₂    is added quickly thereto; the coprecipitation hydrogel forms    instantly.

At the end of this first phase, a hydrated hydrogel containing siliconand/or germanium and a metal—(Si_(x)Ge_(1-x))₄M₃O₁₁, n′H₂O—of gelatinousconsistency is obtained (optionally in the presence of the carboxylatesalt(s) of the formula(e) R8-COOM′ and R9-COOM′ in the case of thesecond variant). The gel has thixotropic behaviour, that is to say itpasses from a viscous state to a liquid state when it is stirred andthen returns to its original state if it is allowed to rest for asufficient time. The hydrogel precursor containing silicon and/orgermanium and a metal therefore also corresponds to formula (II) 4(Si_(x)Ge_(1-x)) 3 M ((10−ε) O) ((2+ε) (OH)), wherein:

-   -   x is a real number of the interval [0; 1], and    -   ε is a real number of the interval [0; 1].

The gel containing silicon and/or germanium and a metal can also berecovered after centrifugation (for example from 3000 to 15,000revolutions per minute for from 5 to 60 minutes) and removal of thesupernatant, optionally washing with demineralised water (for exampletwo successive washings and centrifugations) and then drying, forexample in an oven (60° C., 2 days), by lyophilisation, by spray dryingor also by drying with microwave irradiation. The particles containingsilicon and/or germanium and a metal of the formula(Si_(x)Ge_(1-x))₄M₃O₁₁, n′H₂O can thus be stored in the form of a powderwith a view to a subsequent hydrothermal treatment. The particlesobtained containing silicon and/or germanium and a metal are, ifnecessary, ground by means of a mortar (for example an agate mortar) inorder to obtain a homogeneous powder.

2/—Hydrothermal Treatment of the Gel Containing Silicon and/or Germaniumand a Metal

The gel containing silicon and/or germanium and a metal as obtainedhereinbefore is subjected to a hydrothermal treatment at a temperatureof from 150° C. to 600° C., and especially at a temperature of from 150°C. to 400° C.

In order to carry out the hydrothermal treatment:

-   1. the gel is placed in a reactor (of 400 ml); the water/solid ratio    is optionally adjusted by adding water, especially in order to avoid    calcination of the solid fraction); in order to avoid any problem of    leakage from the reactor, the reactor is filled to ⅔ of its volume,-   2. there is optionally added, with stirring, a solution comprising    at least one carboxylate salt of the formula R8-COOM′, in hydrated    or anhydrous form, X denoting a metal chosen from the group formed    of Na and K, and R₂ being chosen from the group formed of H and    alkyl groups containing fewer than 5 carbon atoms,-   3. the reactor is placed inside an oven or conduction oven at the    reaction temperature (established at from 150° C. to 600° C., in    particular from 150° C. to 400° C.) throughout the treatment (from    30 minutes to 60 days).

At the end of this hydrothermal treatment, a colloidal talcosecomposition comprising phyllosilicate mineral particles, in solution inwater, is obtained.

The carboxylate salt optionally present during the hydrothermaltreatment can be added at the time said hydrothermal treatment iscarried out and/or can be obtained from the precipitation medium of thegel containing silicon and/or germanium and a metal according to thesecond variant for the preparation of the hydrogel containing siliconand/or germanium and a metal. Carrying out the hydrothermal treatment inthe presence of a carboxylate salt allows the reaction of converting thehydrogel containing silicon and/or germanium and a metal into a talcosecomposition comprising phyllosilicate mineral particles to be improved,especially by accelerating it. In the case where the hydrothermaltreatment is carried out in the presence of such a carboxylate salt, atemperature inside the oven or autoclave of from 150° C. to 400° C. issufficient.

At the end of this hydrothermal treatment, the contents of the reactorare recovered after filtration and/or optionally centrifugation (forexample at from 3000 to 15,000 revolutions per minute for from 5 to 60minutes) and removal of the supernatant. The recovered talcosecomposition is optionally dried, for example in an oven (60° C., 2days), by lyophilisation, by spray drying or also by drying withmicrowave irradiation.

At the end of such a hydrothermal treatment there is obtained a dividedsolid composition comprising, for example, particles of synthetic talcof the formula Si₄Mg₃O₁₀(OH)₂.

B/—Method for Preparing a Composition Comprising Functionalised MineralParticles According to the Invention

The mineral particles as prepared hereinbefore, for example particles ofsynthetic talc Si₄Mg₃O₁₀(OH)₂, are brought into contact with a solutioncomprising at least one oxysilane and/or at least one oxygermane havingat least one organic group chosen from the group formed of cationicheteroaryl groups, quaternary ammonium groups and their salts.

The functionalising agent (oxysilane and/or oxygermane) has the chemicalformula:

wherein:

-   -   A denotes said organic group om the group formed of cationic        heteroaryl groups, quaternary ammonium groups and their salts,    -   T is chosen from silicon and germanium, and    -   R1, R2 and R3 are identical or different and are chosen from the        group formed of hydrogen and linear alkyl groups containing from        1 to 3 carbon atom(s).

The functionalising agent can optionally polymerise in thefunctionalising solution and be in a small proportion in the followingform:

or also in the form of other products of that polymerisation.

To that end:

1. 1 gram of phyllosilicate mineral particles previously dried in anoven is placed in 40 ml of an aqueous solution in which there isdissolved at least one functionalised oxysilane and/or at least onefunctionalised oxygermane as defined hereinabove, for 1 hour, withstirring, the concentration of that compound in the solution being, forexample, 0.015 mol/l,

2. the particles are recovered by centrifuging the solution, for examplefor 10 minutes at 10,000 revolutions/minute, and removing thesupernatant solution,

3. the particles are rinsed one to two times with distilled water, bycentrifugation, for example for 10 minutes at 10,000 revolutions/minute,and removal of the supernatant solution each time, so as to removeexcess oxysilanes and/or oxygermanes, and

4. the particles obtained are dried, for example by lyophilisation.

In particular, said oxysilane can be a trialkoxysilane which is solublein an aqueous medium and has the following formula:

wherein:

-   -   R1, R2 and R3 are identical or different and are chosen from        linear alkyl groups containing from 1 to 3 carbon atom(s),    -   R7 is chosen from linear alkyl groups containing from 1 to 18        carbon atom(s),    -   n is an integer from 1 to 5, and    -   X⁻ is an anion, wherein X is chosen from the group formed of        chlorine, iodine and bromine.

It is then possible to carry out an at least partial exchange of theanion X⁻ by at least one anionic species which is different from X⁻ andis chosen from the group formed of the bromide ion Br⁻, the iodide ionI⁻, the bis-trifluoromethanesulfonamide anion, thetrifluoromethanesulfonate anion, the hexafluorophosphate anion, thetetrafluoroborate anion, the acetate anion, the nitrate anion NO₃ ⁻ andthe nitrite anion NO₂ ⁻. Such an exchange by metathesis allows the moreor less hydrophilic or hydrophobic nature of the functionalised mineralparticles that are prepared to be modulated in a customised manner. Itis possible to use, for example, a metal salt such as a silver salt(especially a silver nitrate AgNO₃) or a lithium salt (such as lithiumbis-trifluoromethanesulfonamide, for example).

C/—Analysis and Structural Characterisation

The size and particle size distribution of the phyllosilicate mineralparticles composing them were evaluated by observation by field effectscanning electron microscopy.

It is found that the particle size of the elementary particles variesfrom 20 nm to 100 nm. In particular, the phyllosilicate mineralparticles have a thickness of less than 100 nm and a largest dimensionof less than 10 μm.

Moreover, measurements of the specific surface area (surface area of theparticles relative to a unit of mass) of the mineral particles that wereprepared, determined according to the BET method by the quantity ofnitrogen adsorbed at the surface of said particles so as to form amonomolecular layer covering said surface completely (measurementaccording to the BET method, standard AFNOR X 11—621 and 622) werecarried out. It is found that the specific surface area of thephyllosilicate mineral particles contained in a composition obtained bya method according to the invention is approximately 700 m²/g.

Such a specific surface area value, while the specific surface area of anatural talc is approximately 20 m²/g, is indicative not only of a verysmall particle size and of the lamellar nature of the particles, butalso of the divided or deagglomerated state of the particles, andespecially of an exfoliation of the elementary lamellae forming saidparticles.

EXAMPLE 1

A suspension comprising particles of talc of the formula Si₄Mg₃O₁₀(OH)₂comprising 100 g of talc gel (that is to say 10 g of dry talc) in 300 mlof water is prepared. The suspension is stirred magnetically and at thesame time subjected to ultrasound until a suspension having ahomogeneous consistency and a milky appearance is obtained.

The functionalised oxysilane is then added to the suspension comprisingtalc particles. 1 g of 1-(trimethoxy-silyl-propyl)-3-methyl-imidazoliumchloride previously diluted in 20 ml of water is added. The oxysilaneand the talc particles are thus brought into contact in thefunctionalising solution so that the molar ratio between the oxysilaneand the talc particles is 0.13. Magnetic stirring and sonication aremaintained for 10 minutes.

1-(Trimethoxy-silyl-propyl)-3-methyl-imidazolium chloride has thefollowing structural chemical formula:

The suspension is then centrifuged at 10,000 revolutions/minute for 10minutes, and the supernatant solution composed of water and excessfunctionalised oxysilane.

The functionalised talcose composition that is recovered is thensubjected to washing with demineralised water and centrifugation.

Finally, the talcose composition recovered after centrifugation is driedby lyophilisation (trap at −52° C. and vacuum of 0.087 mbar).

The talcose composition obtained comprises 0.03 mmole of oxysilane pergram of talc (measurement carried out by elemental analysis).

The specific surface area of the talcose composition obtained, measuredaccording to the BET method, is 764 m²/g.

The X-ray diffractogram of the talc composition so obtained is shown inFIG. 1. The X-ray diffractogram of this talcose composition hasdiffraction peaks corresponding to the diffraction peaks of thefunctionalised talc, and in particular the following characteristicdiffraction peaks:

-   -   a plane (001) situated at a distance of 11.074 Å (I=100);    -   a plane (020) situated at a distance of 4.554 Å (I=33);    -   a plane (003) situated at a distance of 3.173 Å (I=67);    -   a plane (060) situated at a distance of 1.512 Å (I=16).

The proton NMR spectrum (FIG. 2) of the mineral particles prepared makesit possible to identify the presence of the Hs of the Mg(OH) groups ofthe talc lamellae (chemical shifts between 0 and 1 ppm), the Hs of theimidazolium ring (chemical shifts between 6 ppm and 9 ppm) and of water(chemical shifts between 3 and 5 ppm).

The carbon NMR spectrum (FIG. 3) of the mineral particles prepared makesit possible to identify the presence of an imidazolium group (chemicalshifts between 115 ppm and 140 ppm) as well as the presence of a methylgroup and of methylene groups (chemical shifts between 0 ppm and 60 ppm,including the methylene of the CH₂—Si bond between 9 ppm and 10 ppm).

The silicon NMR spectrum (FIG. 4) of the mineral particles preparedmakes it possible to identify the presence of Si—O—Si groups (chemicalshifts between −80 ppm and −100 ppm).

The proton, carbon and silicon NMR spectra were obtained with a magneticfield of 9.4 tesla.

FIG. 5 is an image obtained by field effect scanning electron microscopy(SEM-FEG) of the mineral particles prepared.

These analyses therefore show that the functionalisation of the talc issuccessfully carried out by the fixing of an oxysilane carrying animidazolium group by covalent bonding with the talc. They are inparticular bonds of the Si—O—Si type between a silicon atom of the talcand the silicon of the oxysilane. Furthermore, the functionalisedtalcose composition prepared by a method according to the inventioncomprises individualised and deagglomerated talc particles which have avery large specific surface area.

The invention can be the subject of many other applications and ofdifferent variants with respect to the embodiments and examplesdescribed above. In particular, other oxysilanes and oxygermanes canlikewise be used as the functionalising agent for the phyllosilicatemineral particles.

1/ Method for preparing a composition comprising mineral particlesfunctionalised by at least one organic group and having a specificsurface area determined according to the BET method—standard AFNOR X11—621 and 622—of greater than 500 m²/g, wherein: there is chosen acomposition, named the phyllosilicate composition, comprising mineralparticles belonging to the family of the lamellar silicates, saidmineral particles having a thickness of less than 100 nm and a largestdimension of less than 10 μm; there is chosen at least one compound,named the functionalising agent, from the group formed of oxysilanes andoxygermanes having at least one organic group, said phyllosilicatecomposition is brought into contact with a solution, named thefunctionalising solution, comprising said functionalising agent, so asto obtain a phyllosilicate composition comprising mineral particlesfunctionalised by said organic group, characterised in that the organicgroup is chosen from the group formed of cationic heteroaryl groups,quaternary ammonium groups and their salts. 2/ Method according to claim1, characterised in that said functionalising agent has the chemicalformula:

wherein: A denotes said organic group, T is chosen from the group formedof silicon and germanium, and R1, R2 and R3 are identical or differentand are chosen from the group formed of hydrogen and linear alkyl groupscontaining from 1 to 3 carbon atom(s). 3/ Method according to claim 1,said organic group has the chemical formula:

wherein: R7 is chosen from linear or branched alkyl groups containingfrom 1 to 18 carbon atom(s), n is an integer from 3 to 11, X⁻ is ananion chosen from the group formed of the bromide ion, the iodide ion,the chloride ion, the trifluoromethanesulfonate anion, the acetateanion, the nitrate anion and the nitrite anion. 4/ Method according toclaim 3, characterised in that, after said phyllosilicate compositionhas been brought into contact with the functionalising solution, thereis carried out an at least partial exchange of the anion X⁻ by at leastone anionic species which is different from X⁻ and is chosen from thegroup formed of the bromide ion, the iodide ion, thebis(trifluoromethanesulfonyl)amide anion, the trifluoromethanesulfonateanion, the hexafluorophosphate anion, the tetrafluoroborate anion, theacetate anion, the nitrate anion and the nitrite anion. 5/ Methodaccording to claim 3, characterised in that, after said phyllosilicatecomposition has been brought into contact with the functionalisingsolution, there is carried out an at least partial exchange of the anionX⁻, when X is chosen from the group formed of chlorine, bromine andiodine, by adding at least one silver salt. 6/ Method according to claim1, characterised in that said phyllosilicate composition comprisesmineral particles having the chemical formula:(Si_(x)Ge_(1-x))₄M₃O₁₀(OH)₂ Si denoting silicon, Ge denoting germanium,x being a real number of the interval [0; 1], and M denoting a metal. 7/Method according to claim 1, characterised in that said functionalisingagent is chosen from the group formed of oxysilanes and oxygermaneswhich are soluble in an aqueous medium. 8/ Method according to claim 1,characterised in that said functionalising solution is an aqueoussolution. 9/ Method according to claim 1, characterised in that saidmineral particles are chosen from the group of the 2:1 phyllosilicates.10/ Method according to claim 1, characterised in that said mineralparticles are prepared by a hydrothermal treatment of a hydrogelprecursor containing silicon and/or germanium and a metal, said hydrogelprecursor comprising particles of the formula (Si_(x)Ge_(1-x))₄M₃O₁₁,n′H₂O, wherein: Si denotes silicon, Ge denotes germanium, x is a realnumber of the interval [0; 1], M denotes a metal atom, n′ relates to anumber of molecule(s) of water associated with said hydrogel. 11/ Methodaccording to claim 10, characterised in that the hydrogel precursor isprepared by a coprecipitation reaction between: at least one compoundcomprising silicon and/or germanium, such as sodium metasilicate orsodium metagermanate or also silicon, and at least one metal salt, so asto obtain a hydrated hydrogel precursor containing silicon and/orgermanium and a metal comprising 4 silicon and/or germanium atoms for 3atoms of at least one metal M. 12/ Composition obtainable by a methodaccording to claim 1, named phyllosilicate composition, comprisingmineral particles belonging to the family of the lamellar silicates,characterised in that said mineral particles have: a thickness of lessthan 100 nm and a largest dimension of less than 10 μm; a specificsurface area determined according to the BET method—standard AFNOR X11—621 and 622—of greater than 500 m²/g; and at least one organic groupchosen from the group formed of cationic heteroaryl groups, quaternaryammonium groups and their salts. 13/ Phyllosilicate compositionaccording to claim 12, characterised in that it comprises mineralparticles having the chemical formula:(Si_(x)Ge_(1-x))₄M₃O₁₀(OH)₂ Si denoting silicon, Ge denoting germanium,x being a real number of the interval [0; 1], M denoting a metal. 14/Phyllosilicate composition according to claim 12, characterised in thatsaid mineral particles have a specific surface area of greater than 600m²/g. 15/ Method according to claim 2, said organic group has thechemical formula:

wherein: R7 is chosen from linear or branched alkyl groups containingfrom 1 to 18 carbon atom(s), n is an integer from 3 to 11, X⁻ is ananion chosen from the group formed of the bromide ion, the iodide ion,the chloride ion, the trifluoromethanesulfonate anion, the acetateanion, the nitrate anion and the nitrite anion. 16/ Method according toclaim 4, characterised in that, after said phyllosilicate compositionhas been brought into contact with the functionalising solution, thereis carried out an at least partial exchange of the anion X⁻, when X ischosen from the group formed of chlorine, bromine and iodine, by addingat least one silver salt. 17/ Phyllosilicate composition according toclaim 13, characterised in that said mineral particles have a specificsurface area of greater than 600 m²/g.